The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus suitable for plasma surface treatment of a specimen such as thin-film formation, etching, sputtering or plasma oxidation using plasma produced through microwave discharge. The disclosure of the present invention presented here will be made in conjunction with the formation of a thin film on the surface of a specimen by way of example.
The conventional techniques concerning a microwave plasma processing apparatus are disclosed by, for example, JP-A-60-202942 and JP-A-61-284098.
A plasma processing apparatus according to the prior art disclosed by the JP-A-60-202942 is constructed such that the direction of introduction of a microwave and the direction of a magnetic line of force coincide with each other. The conventional plasma processing apparatus having such a construction will now be explained by virtue of the accompanying drawings.
FIG. 1 is a view for explaining the principle of the conventional plasma processing apparatus, and FIG. 2 is a cross section showing the construction of the conventional plasma processing apparatus. In FIGS. 1 and 2, reference numeral 1 designates a microwave, numeral 2 a magnetic line of force, numeral 3 an electron cyclotron resonance (hereinafter referred to as ECR) region, numeral 4 a waveguide, numeral 5 a microwave introducing window, numeral 6 a specimen chamber, numeral 7 a specimen, numeral 8 specimen table, numeral 9 a gas, numeral 10 a vacuum exhaust pipe, and numeral 11 magnetic field generating means.
A magnetic line of force generated by the magnetic field generating means in the conventional plasma processing apparatus is a spreading magnetic field the strength of which becomes gradually weak along the direction of propagation of a microwave. As shown in FIG. 1, in the magnetic line of force and in the course of the propagation path of the microwave is produced a thin ECR region the longitudinal direction or plane of which is orthogonal to the magnetic line of force and the direction of propagation of the microwave. More particularly, as shown in FIG. 2, the conventional plasma processing apparatus comprises the specimen chamber 6 which is vacuum-exhausted by an exhaust device (not shown) through the vacuum exhaust pipe 10, a microwave introducing means which includes the waveguide 4 for guiding the microwave 1 and the microwave introducing window 5 formed at an upper portion of the specimen chamber 6 for introducing the guided microwave into the specimen chamber 6, and the magnetic field generating means 11 which is provided outside the specimen chamber 6 for generating the magnetic line of force 2 to produce an ECR. The specimen table 8 for holding thereon the specimen 7 to be treated is placed in the specimen chamber 6. The specimen chamber 6 is constructed such that the gas 9 necessary for the treatment of the specimen 7 can be introduced into the specimen chamber 6. In the plasma processing apparatus thus constructed, the ECR region 3 is generated in a space above the specimen 7 and plasma produced in the ECR region 3 reaches a surface of the specimen 7 so that the specimen 7 is subjected to a predetermined treatment.
The above-mentioned conventional plasma processing apparatus has a problem that the efficiency of absorption efficiency of the microwave energy in the ECR region 3 is poor since the depth or thickness l of the ECR region 3 generated by virtue of the magnetic line of force 2 is very small and the microwave 1 progresses in the direction of the depth l of the ECR region. Also, in the case where it is desired to apply an electric field of an RF power source to the specimen table 8 and if a counter electrode is provided at the introducing side of the microwave of the microwave introducing window 5 above the specimen 7, the energy of the microwave 1 is inconveniently intercepted by the counter electrode and a pattern of the counter electrode appears on a film formed on the specimen 7 since the microwave introducing window 5 is provided at an upper portion of the specimen chamber 6 or above the specimen 7. Accordingly, it is not possible to uniformly extend the counter electrode above the specimen 7. Therefore, the conventional plasma processing apparatus involves a problem that it is not possible to have the AC electric field uniformly act on the specimen 7 to a desired uniform treatment, for example, a film formed on the surface of the specimen 7 has a non-uniform thickness distribution.
A plasma processing apparatus according to the prior art disclosed by the JP-A-61-284098 includes a transverse magnetic field type of microwave plasma discharge device in which a microwave to be introduced into a plasma generating chamber is made orthogonal to a magnetic line of force. However, in the JP-A-61-284098 there is an ECR region in the plasma generating chamber, and the generated plasma is led to a specimen chamber and thereby a thin film is formed. There is a problem that as there is the ECR region in the plasma generating chamber far from a specimen table, ions and radicals are lost during the plasma transmission. Therefore, the formation of a thin film on the surface of a specimen by virtue of radicals and ions cannot be effected.